Ophthalmic lenses are formed from glass or plastics. Plastics include, for example, polymers based on allyl diglycolcarbonate monomers and polycarbonates. Ophthalmic lenses are formed as a single integral body or as laminated lenses that are fabricated by bonding two lens wafers (i.e., a front wafer and a back wafer) together with a transparent adhesive. Laminated lens wafers are described, for example, in U.S. Pat. Nos. 5,149,181, 4,857,553, and 4,645,317.
Commercially available plastic ophthalmic lenses are commonly coated with a thin polymeric scratch resistance coating. The thickness of the polymeric scratch resistance coating will depend, in part, on the substrate material. Abrasion resistant radiation curable coatings for polycarbonate substrates are described, for example, in U.S. Pat. No. 4,954,591. The vast majority of ophthalmic lenses are clear.
Absorption of ultraviolet radiation, especially those having higher wavelengths, by the retina is believed to accelerate or cause retinal injuries such as macular degeneration. Specifically, epidemiological data correlates UV sunlight exposure with the incidence of lenticular opacities (cataracts) and possibly with pseudo-exfoliation in the eyes.
Consequently, there is a demand for finished eyeglass lenses, including sunglasses, with UV-A, absorption capabilities. Conventional methods of fabricating plastic lenses with UV protection have added UV absorbers into the casting monomer systems that form the ophthalmic lenses. Unfortunately, UV absorbers can interact with the casting monomer system thereby blocking complete polymerization. This results in a variety of lens defects including softness. The effect is exacerbated in prescription lenses where the thicker regions of the lens will emit a more intense yellow color. The lens will provide UV-A protection but will be aesthetically undesirable.
U.S. Pat. No. 5,013,608 describes a coating composition containing at least about 3% to about 20% (wt) of coating solids of a tintability enhancing compound (i.e., UV absorbers) in a base resin comprising an aqueous, aqueous-alcoholic, or alcoholic dispersion of colloidal silica, or a mixture of colloidal silica with a metal oxide, and a partial condensate of an epoxy-functional silanol which is blended with a partial condensate of another silanol. A crosslinking agent and a curing catalyst are added to form purportedly highly tintable abrasion resistant coating compositions. The coating composition upon curing is alleged to form hard films that provide both abrasion resistance and high levels of tinting and, optionally, absorbance of ultraviolet radiation. Although this coating composition may be suitable for fabricating tinted articles such as sunglasses, it is not suitable for fabricating non-tinted articles. The reason is that these hard films invariably exhibit a yellowish hue.
U.S. Pat. No. 5,371,138 describes a UV absorbing polysiloxane resin composition for coating transparent sheets and plastic spectacle lenses. It is formed by adding water-based colloidal silica to a silanol blend, heating, incorporating additives and incorporating a UV absorbing material such as 2,2',4,4'-tetrahydroxy-benzophenone, benzothiazoles and benzotriazoles, U.S. Pat. No. 4,233,441 describes an acryloxybenzothiazole copolymerizable UV light absorber that can be copolymerized with monomers and oligomers by free radical or radiation curing. JP Patent 55093447 describes polycarbonate articles that are coated with an adhesive and an overcoat, which contains a benzotriazole-type UV absorber. This apparently prevents the substrate from dusting, alkali and solvent attack, and yellowing. U.S. Pat. No. 4,216,267 describes a laminate that comprises a sheet of clear PVC or polycarbonate with a 0.1-10 mil thick coating of an acrylic polyurethane and an acrylic UV absorber. U.S. Pat. No. 4,202,834 describes a copolymerizable UV light absorber, cyanodiphenyl-acryloxy-alkyl-allyl or substituted allyl ether, purportedly useful in providing UV protection to radiation cured coatings. U.S. Pat. No. 4,284,485 describes a polyalkylpiperidine derivative as a UV absorber useful in coatings that are applied to various materials. JP Patent 50054670 describes polycarbonate moldings coated with solutions prepared by mixing siloxanes and UV absorbers (benzophenones, triazoles, and salicylates). A preferred UV absorber is 2-hydroxy-4-octoxybenzophenone is claimed as one of the examples. U.S. Pat. No. 5,013,608 describes a coating composition containing 3-20% by weight (of coating solids) of a UV absorber used as a tintability enhancer.
As is apparent, the prior art methods of fabricating films with UV radiation blocking properties are deficient in a number of respects. First, for UV absorbers which are colorless or nearly colorless, UV blocking is incomplete in the UV-range of 290 nm-380 nm and at longer wavelengths. These UV absorbers exhibit maximum absorption at relatively short wavelengths in the UV spectrum. Subsequently, these UV absorbers have the undesirable side effect of imparting a yellow hue to the coating at the concentrations needed for full UV blocking at these ranges. UV absorbers demonstrating incomplete UV-A blocking include acrylics, benzothiazoles and benzotriazoles, HALS (hindered amino light absorbers), monohydroxy benzophenones and salicylates.
Second, when a UV absorber is capable of blocking the full UV-A range due to an absorption maximum at relatively long UV wavelengths, the UV absorber is yellow and imparts a yellow hue to the coating. This is caused by the absorption of visible light, particularly in the blue region (wavelengths above 400 nm) by these UV absorbers. This is particularly problematic for ophthalmic lenses where coatings are relative thin, e.g., from 0.1 .mu.m to 25 .mu.m, and if full blocking of the UV-A range or at longer wavelengths is desired, the UV absorbers must have a strong absorption in those wavelength ranges. UV-A absorbers in this latter category include the dihydroxy benzophenones such as 2,2',4,4'-tetrahydroxy-benzophenone.